The right of self-defense derives from natural law theory, which this UN bureaucrat is discarding in favor of positivism (as you noted).

My point, however unclear, was that the Progs have no internal philosophical consistency in terms of their legal reasoning, just their ideological objectives. On other issues, say nuclear disarmament or the precedence of their argument over national law, they readily invoke natural law. Any tool that gets them to the " right" result at the moment is acceptable.